I. Field of the Invention
The present invention relates generally to polycrystalline diamond bearings for supporting the drive shaft of a downhole well drilling motor and more particularly to the support structure for such bearings.
II. Description of the Prior Art
Polycrystalline diamond (PCD) bearings have found application in oil drilling and other environments demanding high load carrying ability under extreme wear conditions.
The use of PCD inserts in thrust bearings is specifically described in U.S. Pat. Nos. 4,468,138; 4,620,601; 4,708,496; 4,720,199; 4,732,491; and 4,789,251.
In the prior art, these thrust bearings usually consisted of a pair of annular steel plates each supporting a plurality of cylindrical tungsten carbide studs having disc-shaped diamond bearings mounted thereon. Such bearing arrangements were unsealed since the bearings were lubricated and cooled by the flow of mud therethrough.
Such designs have worked quite well and have dramatically improved the lifetime of motor bearings. In fact, the diamond bearings have worked so well and lasted so long during operation that a problem has arisen with erosion of the support structure at the base of the cylindrical studs. This, of course, is caused by the mud passing around the studs. Because of such erosion, the studs would eventually break away from the bearing assembly even though the diamond surface was barely worn.
Various steps have been taken to alleviate this problem but none of these steps have been totally satisfactory.
One solution to the problem was to provide hardfacing to the support ring. Although improved results were obtained, erosion still occurred.